1

Big History: An Overview

Light echo around V838 Monocerotis, by NASA, ESA and H.E. Bond (STScI), CC0.

By John Green, adapted by Newsela.

History is an attempt to understand both our insignificance and our significance. To study history is to better understand the world and your place in it.

950L

BIG HISTORY PROJECT BIG HISTORY: AN OVERVIEW 2

You are very small. You are one of several billion living members of your species. The planet you live on is only the fifth-largest planet orbiting a star we call the Sun. There are more than a hundred billion such stars in our galaxy, and perhaps a hundred billion galaxies in the Universe. It’s almost impossible to grasp your smallness. There are more stars in the Universe than there are grains of sand on Earth.

Yet, you are also very large. You’re a member of an extraordinarily powerful species that has reshaped our planet. You are physically vast as well: Your body contains trillions of cells and is colonized by trillions more microscopic organisms.

What Is History? History is the attempt to better understand the world we live in and our place in it. You and every other living human are the latest chapter of the human story. Everything that has happened so far has led up to this point.

What Is Big History? Yet, there’s a lot more to history than the human story. If you think of history as the story of life on Earth, almost all of it played out before our species (Homo sapiens) showed up on the scene. After all, we’ve been around only for the last 250,000 or so years. That is less than 0.01 percent of the history of life on Earth.

Thresholds of Increasing Complexity

Because the scale of Big History is so vast, it is impossible to cover everything. All historians have to make choices about what to include and what to leave out in the stories they tell. So, what does the story of Big History focus on? Big Historians focus on eight turning points in the history of the Universe. These are called thresholds. They are moments when the Universe or our world became significantly more complex than it had been previously.

Threshold 1: The Big Bang

About 13.8 billion years ago, the Universe was created in a “big bang.”

This Big Bang was a split second in which all matter and energy expanded at enormous speed and became the Universe. What was there before the Big Bang? It’s mind-bending to think about, but in some ways, there was no “before” the Big Bang. The Big Bang created not only space but also time. The important thing to know is that around 13.8 billion years ago, very suddenly, the Universe exploded into being.

Threshold 2: The Stars Light Up

After the Big Bang, the Universe expanded and cooled. It took around 380,000 years, but eventually, it was cool enough for the simplest atoms, hydrogen and helium, to form. For a very long time, the Universe consisted almost entirely of hydrogen and helium. After a few hundred million years, clouds of hydrogen and helium began to collapse, and the increasing heat and pressure this generated led to the creation of the first stars. Stars represent the second threshold of increasing complexity in Big History. Not only are stars more complex than simple atoms, but they are also able to create enormous amounts of energy. Over time, gravity grouped stars into galaxies, which created further complexity in the Universe.

BIG HISTORY PROJECT BIG HISTORY: AN OVERVIEW 3

Threshold 3: New Chemical Elements

Stars made the Universe more complex, but the Universe still consisted primarily of hydrogen and helium. This changed when the first generation of stars died. The death of a star can generate high temperatures and pressures like those in the Big Bang, and this makes possible the creation of more complex atoms. A greater variety of atoms is critical to making more complex things like planets and living things. Thus, the death of stars is the third threshold of increasing complexity in Big History.

Threshold 4: Earth and the Solar System

Our Sun is a star, and like all other stars, it was formed from the collapse of a huge cloud of gas and dust particles. More than 99 percent of this material went to make up the Sun, but thin strands, or wisps, of matter orbited around it at various distances. Over time, the matter in each orbit was drawn together by gravity. The gravitational pull created lumps of matter that eventually formed the planets. This process is called accretion. It is how our Earth was formed around 4.5 billion years ago.

Threshold 5: Life

On the floor of Earth’s oceans, there are volcanic vents that release heat from deep underground. Around these vents, complex chemicals long engaged in ever-changing reactions powered by the escaping heat. Those reactions led to the formation of the first living organisms. The earliest consisted of single cells, as most living organisms do even today. Like all living organisms, those early single-celled creatures were subject to the laws of evolution. Generation by generation, the average features of species slowly changed. Eventually, entirely new species were formed.

For a very long time, that was it: single-celled, microscopic organisms. Life first emerged on Earth 3 billion years ago, but the first multicellular life didn’t show up until around 1 billion years ago. But slowly, life grew more and more complex, and large, multi-cellular organisms eventually spread, not only in water but also on land.

One hundred million years ago, the reptiles we call dinosaurs ruled the land. About 65 million years ago, however, most of them died off. Now other types of large animals could take their place. In the last 65 million years, the most successful of all has been the large class of animals called mammals.

Threshold 6: Collective Learning

The extinction of the dinosaurs allowed mammals, including primates, to evolve and eventually dominate the Earth. Our ancestors, the hominins, are primates. They first appeared between 5 million and 7 million years ago in Africa. Over millions of years, hominins evolved in important ways, both physically and socially. About 200,000 years

BIG HISTORY PROJECT BIG HISTORY: AN OVERVIEW 4

ago, Homo sapiens, which means “wise human,” appeared. Modern humans developed language, which allowed them to share complex ideas and pass on knowledge from generation to generation. This process is known as collective learning.

Threshold 7: Agriculture

Our ancestors survived by foraging — hunting animals and gathering plants. Foraging supported early humans for millions of years. About 12,000 years ago, humans began to farm. The development of agriculture brought major lifestyle changes. Because foraging for survival was no longer necessary, people were able to live in settled communities. This allowed for the growth of cities, more complex political structures, and the rise of specialized skills and trades.

Threshold 8: Modern Revolution

Starting about 300 years ago, the pace of technological change became much more rapid. This led to a period we call the modern revolution. The rapid growth of the human population and the creation of a highly interconnected world are some of the key changes the modern revolution brought. So far, the modern revolution is Big History’s final threshold.

What’s Next? The story of the Universe isn’t only about the past. We know this story doesn’t end with Threshold 8. So, what’s next? What might the next threshold of increasing complexity be? When you reach the end of this course, you’ll be able to make some informed guesses about the future.

But first, let’s really dig into what got us here.

BIG HISTORY PROJECT BIG HISTORY: AN OVERVIEW 5

Articles leveled by Newsela have been adjusted along several dimensions of text complexity including sentence structure, vocabulary and organization. The number followed by L indicates the Lexile measure of the article. For more information on Lexile measures and how they correspond to grade levels: http://www.lexile.com/about-lexile/lexile-overview/

To learn more about Newsela, visit www.newsela.com/about.

The Lexile® Framework for ReadingThe Lexile® Framework for Reading evaluates reading ability and text complexity on the same developmental scale. Unlike other measurement systems, the Lexile Framework determines reading ability based on actual assessments, rather than generalized age or grade levels. Recognized as the standard for matching readers with texts, tens of millions of students worldwide receive a Lexile measure that helps them find targeted readings from the more than 100 million articles, books and websites that have been measured. Lexile measures connect learn-ers of all ages with resources at the right level of challenge and monitors their progress toward state and national proficiency standards. More information about the Lexile® Framework can be found at www.Lexile.com.